Mittoo. He and Clement Dodd received credit on the song as co-writers. It was described to have a "cod-reggae groove that smoulders like a barbecue", as a guitar and piano were used for the background music, following the notes Gm—F as its basic chord progression. It is set in the time signature of common time, having a metronome of 96 beats per minute, and is played in the key of F major. Lyrically, the song describes Allen's satisfaction in her former lover's suffering, being in a vengeful mood: "At worst / I feel bad for a while, / But then I just smile / I go ahead and smile," thus creating a contrast between "the peppy melody and brassy lyrics". The inspiration for the song came from a real life experience, when Allen broke up with her then boyfriend, Lester Lloyd, resulting in a drug overdose and hospitalization for her depression. The singer claimed "I started to get depressed and anyone who suffers from depression knows that it can soon get so bad that you can't get out of bed. It was then that I checked into the Priory. That was really tough as I was an emotional mess. [...] The lyrics are definitely bitter-sweet". Allen said she later regretted the direct approach of her lyrics: I'm now less inclined to do that, because everything that I do say gets repeated in a way that I haven't said it, or taken out of context and spun in some negative way — and it makes me really sad. I'm not, like, a negative person. I'm actually quite positive, but this industry has really made me feel angry and negative recently. I'm not enjoying it at the moment. Critical reception "Smile" was met with mixed to positive reviews from music critics. According to Heather Phares of AllMusic, the song "has a silky verse melody that just barely conceals [the singer's] spite", while she keeps "her revenge sweet, the extra sting being given to it by the way she sounds like she's singing about how ice cream or puppies or being in love makes her smile". Blender reporter Jon Dolan claims that Allen "deploys a sugary melody as a Trojan horse for a smackdown on a douche-bag ex-boyfriend", as Rob Webb from Drowned in Sound called "Smile" an "infectious slice of bouncing, carnival reggae that punches hard with its opening line: 'When you